The process for recovery of copper metal values from ores and processing liquids by solvent extraction-electrowinning (hereafter, "SX-EW") is well-known. Briefly, the process is carried out using a copper-bearing aqueous solution which is obtained by dissolving (generally from an ore) the copper in an aqueous leach liquor, or by using a copper-bearing solution such as process effluent. The resulting solution of copper values is mixed with a water-immiscible organic solvent (e.g., kerosene) containing a water-insoluble ion exchange composition having selective affinity for the copper values. The ion exchange composition preferentially extracts the copper values from the aqueous solution. The aqueous and organic phases are separated. The aqueous solution, now copper-depleted, is usually referred to as "raffinate." The raffinate can be recycled as leach liquor (in a leaching process) or discarded (in a process such as recovery of copper from process effluent). The organic phase (which contains ion exchange composition and the extracted copper values) is usually referred to as "loaded organic." The desired copper values are removed from the loaded organic by mixing with an aqueous strip solution containing strong acid such as sulfuric, phosphoric, or perchloric acid, and having lower pH than the above copper-bearing aqueous solution. The aqueous strip solution extracts the desired copper values from the loaded organic. After separation of the organic and aqueous phases, the desired copper values are present in the aqueous strip solution. The resulting copper-rich aqueous strip solution is usually referred to as an "electrolyte" or "rich electrolyte." The copper-depleted organic phase is usually referred to as a "barren organic." The barren organic can be recycled.
Copper is recovered in purified form from the electrolyte by a technique known as "electrowinning" (hereafter sometimes referred to as "EW"). The electrowinning process typically involves plating the copper on copper starting sheets or stainless steel cathode mother blanks. The plating cycle usually takes about seven days to obtain a 100-pound cathode from each side of the mother blank. The cathodes are stripped mechanically from each side of the mother blank and are then available for further processing which can include drawing, rolling, etc. Often these cathodes are transported to a rod plant wherein they are subjected to continuous casting. After recovery of the desired copper, the copper-depleted electrolyte, which is sometimes referred to as "lean electrolyte," can be recycled as aqueous strip solution for fresh loading with copper values.
The production of copper foil by electrodeposition involves the use of an electroforming cell containing an anode, a cathode, an electrolyte solution containing copper ions and sulfate ions, and a source of current. Through the application of voltage between the anode and the cathode the deposition of copper is effected on the cathode surface. The process begins with the copper feed stock which is dissolved in sulfuric acid to form the electrolyte solution. The feedstock is an electrolytically purified form of copper such as copper shot, copper wire, copper oxide or recycled copper. The resulting copper sulfate solution is then purified in order to ensure that high purity copper sulfate required for the production of foil is generated. Various types of agents for controlling the properties of the foil such as animal glue and thiourea can be added to the electrolyte solution. The electrolyte solution is pumped into the electroforming cell, and with the application of voltage between the anode and cathode, the electrodeposition of copper takes place. Typically the process involves using cylindrical cathodes that may be of varying diameters and widths. The anodes conform to the curvature of the cathodes so as to maintain a constant separation or gap between the two.
The electrolytically purified copper feedstocks used in prior art electrodeposition processes are often produced using SX-EW techniques of the type discussed above. They are also made using traditional smelting and refining techniques. The prior art electrodeposition processes, which involve initially dissolving the copper feedstock in a digester to form copper ions, are slow, difficult to control, and require large quantities of expensive pure copper inventoried in the digester. It would be advantageous if copper foil could be produced directly from relatively impure sources of copper such as copper ore or copper-containing waste without the additional steps of first recovering pure copper using electrolysis and then dissolving the pure copper to obtain copper ions for the electrolyte solution. The present invention provides such an advantage.
By virtue of the inventive process copper foil is produced using fewer manipulative steps when compared to prior art practices. The inventive process utilizes a copper source that does not require in its production the additional steps of electrowinning, drawing, etc., which are used in making the electrolytically purified copper feedstocks (e.g., copper shot, copper wire, copper oxide, recycled copper, etc.) used in the prior art. Also, the inventive process does not require the use of the digestion step used at the commencement of prior art electrodeposition processes. Impurities carried from the extraction steps used in the inventive process to the electrolyte solution of the process do not degrade the performance characteristics of the copper foil. Copper foil made by the inventive process is produced in a simplified and less costly manner when compared to the prior art.